1. Purpose There can be many physiologic changes during laparoscopic surgery. Increase of intracerebral pressure (ICP) is one of them, which has known to be associated with arterial concentration of carbon dioxide or positional changes. Changes of ICP can be measured directly by invasive method. However, optic nerve sheath diameter (ONSD) has correlation with ICP and ultrasonographic measurement of optic nerve sheath diameter (ONSD) is known to be a noninvasive and rapidly applicable technique for evaluating ICP. The aim of this study is to investigate the change of ONSD according to the positional change during laparoscopic surgery.